Normally, in the case where an electric motor is used to generate motive energy for translational movement, a ball screw device (including a screw drive transmission device) is used to change the rotary movement of the electric motor to one of translational movement.
The example of the ball screw device is a structure comprising a screw axis, with the outer circumference being a helical-shaped groove (hereinafter referred to as “helical groove”) in which for the balls of the device can roll and move, with a nut having a helical groove on the inner circumference screwed onto the screw axis, thus allowing the balls to roll and move in an aligned orbit formed by the groove of the screw axis and not opposed to each other, thus forming a circuit running from one end of the groove to the other end, to allow the balls to circulate unlimitedly.
Prior arts comprising the same type of circuit as this invention are disclosed in Reference Document 1 (Japanese Published Unexamined Application No. H11-270648), referred to below.
As shown in FIG. 1 of Reference Document 1, the ball screw device is a structure having grooves (2a) (3a) spirally formed on a shaft screw (2) and a nut screw (3), respectively, to allow the balls (4) to roll and move. As a ball (4) moves along the groove (3a), the ball (4) is lead to a return groove (5a) within the deflector (5) fixed in the deflector mounting window (3c) and rises through the groove (3a) in an axis direction to allow the balls to circulate (4) unlimitedly.
As shown in FIGS. 3 to 6 of Reference Document 2 (Japanese Published Unexamined Application No. 2007-24229), which is an improved version of the invention of Reference Document 1, an orbit (26) is formed by a helical groove (23) provided on the outer surface of a screw (22) and by a helical groove (24) provided on the inner surface of a nut (25), thus allowing the nut (25) to rotate and move, and forming a circuit (28) congruent with the orbit (26). The circuit (28) is a structure consisting of a tunnel raceway (29) extending from one end (24a) of the groove (24) to the other end. (24b) of the groove (24) within the inner wall of the nut (25). Guiding points (31a) and (31b), respectively, are provided on either end of the tunnel raceway (29).
The invention of Reference Document 2 comprising the aforementioned structure, resolves the following problems that the invention of Reference Document 1 ever has: that an error, or machining error will occur in the engaging (mounting and releasing) structures of the deflector (5) and the discrete component part, i.e. the window portion (3a) and between the return groove (5a) and the screw groove (3a), thus requiring alteration or reprocessing: that the number of component parts will increase, and the time consumed and the cost for maintenance will increase due to further manufacturing and maintenance control, such as further assembling, alteration, and reprocessing or the like.    Reference 1: Japanese Published Unexamined Application No. H11-270648, Paragraph Nos. 0025 to 0029 & FIG. 2)    Reference 2: Japanese Published Unexamined Application No. 2007-24229, Paragraph Nos. 0023 to 0025 & FIGS. 2 to 6)